This invention relates to a process and to a system for the deposition of inorganic materials, and more particularly to the deposition of inorganic dielectric materials onto a semiconductor substrate.
The deposition of inorganic materials, particularly dielectric materials, onto elemental and compound semiconductor substrates has provoked considerable interest in recent years. In semiconductor device fabrication dielectric films have a wide variety of potential applications such as gates, isolation and passivation materials. This expanding technology requires new materials if future growth is to continue. Some current materials under particular investigation include alkaline earth fluorides such as calcium fluoride, barium fluoride, strontium fluoride, mixtures thereof, and the like. Alkaline earth fluorides are of particular interest because they are closely compatible individually or as mixtures with substrate materials typically used in the semiconductor industry such as silicon and the like. Another aspect of this technology relates to the adaptation of inorganic material deposition to a production environment so that substantially high throughputs can be achieved.
In a paper delivered in 1987 entitled, "In-Situ Rapid Isothermal Processing (RIP) of Thin CaF2 films on Silicon (100)" S. Ananda Kugan, et al. described the use of Group II-A fluorides to produce epitaxial dielectric films on silicon and compound semiconductors. In their process, epitaxial dielectric films were deposited in an E-beam system at room temperature and subsequently subjected to in-situ rapid isothermal annealing using incoherent light sources incorporated in the E-beam system. Electrical and structural properties of thin CaF2 films (100 to 1000 Angstroms) deposited on silicon (100) were presented.
The pioneering work on fluorides of barium, strontium, calcium and magnesium in a fluoride vaporization system was described in a paper by R. F. C. Farrow, et al. in the J. Vac. Sci. Technol., Volume 19, No. 3, September/October 1981. The work described included condensation of BaF2 and CaF2 beams in ultraviolet light, onto room temperature surfaces of semiconductors, such as silicon and the like, to produce stoichiometric, polycrystalline, fluorite structure films with little or no preferred orientation.
Another article directed to Group IIA, Fluoride Semiconductor Systems, entitled "MeV Ion Channeling Study of Caf2/Si(111) Epitaxy" in J. Vac. Sci. Technol., A, Volume 4, No. 3, May/June 1986, describes deposition using high-energy electron beam technology. The article states that it is well known for calcium fluoride to be damaged by exposure to high energy E-beams. In fact, it is commonly observed that the normally transparent calcium fluoride layers are colored after exposure to the electron beam due to the formation of color centers.
Finally, an article entitled, "Epitaxial Dielectrics for Ultra-Large Scale Integration (ULSI) and Three-Dimensional IC's" by F. Radpour, et al., at the First International Symposium on ULSI held in May of 1987, describes the development of a reduced thermal budget processing technique for the deposition of epitaxial dielectric films on silicon and compound semiconductors was described. This new technique comprises room temperature deposition of epitaxial dielectrics followed by in-situ rapid isothermal annealing. Calcium fluoride films on silicon substrates were studied. The electron beam system was modified to include a rapid isothermal processor. The processor essentially consisted of high-intensity tungsten-halogen lamps housed in a vacuum deposition chamber.
Although inorganic films have been deposited onto silicon wafers and compound semiconductors, the deposition of the inorganic material has in general not been uniform. The results and experimental apparatus and methods used thus far are not suited to the fabrication of semiconductor products on a production basis.
Therefore, a need exists for a deposition process and apparatus which will uniformly deposit inorganic dielectric materials, particularly materials such as alkaline earth fluorides, onto semiconductor substrates, particularly on an efficient and effective production basis.